Cresylic acid is an important commercial product widely used in the manufacture of chemical, agrichemical, pharmaceutical and industrial intermediate products. The lowest molecular weight member of the cresylic acid family--phenol--is produced synthetically in very large quantities. The three cresols also are produced synthetically, but in much smaller quantities. The di-methyl phenols (xylenols) and other alkylated phenols are not commercially synthesized to any appreciable extent. Therefore, recovery from natural sources such as partially refined petroleum and coal via cooking, gasification, and liquefaction provides the majority of cresylic acid used in industry today. Cresylic acids recovered from these sources are heavily contaminated with aromatic organic compounds including hydrocarbons as well as those containing hetero-atoms such as nitrogen, sulfur and oxygen. Methoxy substituted phenols comprise a particularly troublesome group derived from some low grade coals such as brown coal or lignite. Guaiacol--methoxy phenol--boils near the boiling points of meta- and para-cresol and methyl guaiacols--methoxy cresols--boil in the range of the xylenols. Therefore, the guaiacol cannot be separated from the cresylic acid fractions by conventional distillation. To be useful, the various isomers of cresylic acid must be separated from the other impurities and often from each other, and therein lies the problem because, heretofore there has been no simple process for physically separating guaiacols from cresylic acid. Therefore, the guaiacol must be destroyed in the presence of the cresylic acid which also presents a problem of cresylic acid yield loss. The crude cresylic acid mixture obtained from lignite contains larger amounts of guaiacol than the mixture obtained from coal, up to almost 4% by weight, or even more. Heretofore, such destruction has been accomplished only with difficulty and the resultant loss of cresylic acid yield to byproducts, most of them unwanted heavies and coke.
Considerable academic effort has been reported relating to removal of methoxy compounds or the demethylation of phenols. This work is reported in articles, such as Lawson, J. and M. Klein, Influence of Water on Guaiacol Pyrolysis, Ind. Eng. Chem. Fundam., 24: 203, 1985; Ceylan, R. and J. Bredenberg, "Hydrogenolysis and Hydrocracking of the Carbon-Oxygen Bond. 2. Thermal Cleavage of the Carbon-Oxygen Bond in Guaiacol," Fuel, 61:377, 1982; and Vuori, A. and J. Bredenberg, "Hydrogenolysis and Hydrocracking of the Carbon-Oxygen Bond. 4. Thermal and Catalytic Hydrogenolysis of 4-Propylguaiacol," Holzforschung, 38:133, 1984.
The Lawson article discussed the pyrolysis at 383.degree. C. of guaiacol, neat and in the presence of water to study the effect of the presence of water on char and byproducts formation during the pyrolysis. The byproducts produced were investigated, verifying information found in the Ceylan and Vuori articles cited above. Batch reactors, 98% pure guaiacol and isothermal conditions were employed. The reactor was removed from heat after reaction times of from 15 to 90 minutes and cooled with water and the products analyzed. The presence of water decreased the formation of coke but also disclosed increased catechol yield with o-cresol yield being decreased with the increased amount of added water. The article confirms that when fission occurs, it is the weaker phenoxy-methyl bond which breaks, resulting in phenol and methane products. However, it was found by the inventors of this invention that the pyrolysis at the temperatures disclosed in the articles does not reduce the guaiacol composition of a crude cresylic acid feed stream derived from coal, much less lignite. Such academic discussion therefore, is no help to develop a process for the removal of guaiacol from such feedstreams to recover the cresylic acid. Prior art does point out the problem of byproduct creation during reaction of such heterogeneous streams but offers no real solution to the problem.